Marshall Mg30gfx Guitar Combo Amplifier In Black And Gold A electric guitar pickup is actually much like a dynamic microphone coil. For many years, active microphones have been sent with the style coil mounted on the primary of the microphone's transformer, and not called to surface (‘floating'). The microphone's case is typically linked to the wire shield, which can be attached to the microphone amplifier's ground (see Rane's web site for more discussion).
By and big, active microphones are very calm products consequently of the mix of transformer isolation and balanced, suspended sign lines throughout, as well as protected, humbucking coils.
So why don't you instruments? Instruments are notoriously affected by noise. Humbucking pickups are just an incomplete (though essential!) solution. Well-known solution is always to float the guitar pickup to a balanced result, being a microphone. The same idea was printed this 2001 patent application like this Marshall Mg30gfx Guitar Combo Amplifier In Black And Gold?